Better mpg with 4.56 gears???
Registered User
Joined: Oct 2008
Posts: 49
Likes: 0
From: Vidor, Texas
Anyone who thinks Dodge Ram with a 5.7 engine a 4.56 gear will get more MPG than a identical Ram with a 3.55 gear......NEEDS TO THROW THE CRACK PIPE AGAINST THE WALL, AND WALK A WAY.
That been said, there are some vehicles that could benifit from a gear swap
1. A vehicle that had a larger than factory tire, example 31" to a 33" (all you would be doing would be getting some of the original gearing back), plus you have to overcome the weight of the larger tire.
2. A vehicle with a small engine (in come cases). A good example is TJ Jeep the 2.5 (inline 4) only came with 4.10 gears, the 4.0 (inline 6) came standard with 3.08 gears. I have owned both, me and dodge say they get about the same mileage.
As far as MPG with larger tires, you can change your speedometer calibration, however there is still the fact that your turning a larger heaver tire and rim. This will affect the actual MPG.
That been said, there are some vehicles that could benifit from a gear swap
1. A vehicle that had a larger than factory tire, example 31" to a 33" (all you would be doing would be getting some of the original gearing back), plus you have to overcome the weight of the larger tire.
2. A vehicle with a small engine (in come cases). A good example is TJ Jeep the 2.5 (inline 4) only came with 4.10 gears, the 4.0 (inline 6) came standard with 3.08 gears. I have owned both, me and dodge say they get about the same mileage.
As far as MPG with larger tires, you can change your speedometer calibration, however there is still the fact that your turning a larger heaver tire and rim. This will affect the actual MPG.
All Star
Joined: Jan 2005
Posts: 852
Likes: 4
From: EULESS TEXAS DFW
Anyone who thinks Dodge Ram with a 5.7 engine a 4.56 gear will get more MPG than a identical Ram with a 3.55 gear......NEEDS TO THROW THE CRACK PIPE AGAINST THE WALL, AND WALK A WAY.
That been said, there are some vehicles that could benifit from a gear swap
1. A vehicle that had a larger than factory tire, example 31" to a 33" (all you would be doing would be getting some of the original gearing back), plus you have to overcome the weight of the larger tire.
2. A vehicle with a small engine (in come cases). A good example is TJ Jeep the 2.5 (inline 4) only came with 4.10 gears, the 4.0 (inline 6) came standard with 3.08 gears. I have owned both, me and dodge say they get about the same mileage.
As far as MPG with larger tires, you can change your speedometer calibration, however there is still the fact that your turning a larger heaver tire and rim. This will affect the actual MPG.
That been said, there are some vehicles that could benifit from a gear swap
1. A vehicle that had a larger than factory tire, example 31" to a 33" (all you would be doing would be getting some of the original gearing back), plus you have to overcome the weight of the larger tire.
2. A vehicle with a small engine (in come cases). A good example is TJ Jeep the 2.5 (inline 4) only came with 4.10 gears, the 4.0 (inline 6) came standard with 3.08 gears. I have owned both, me and dodge say they get about the same mileage.
As far as MPG with larger tires, you can change your speedometer calibration, however there is still the fact that your turning a larger heaver tire and rim. This will affect the actual MPG.
I will help you out... our trucks come from the factory OVERDRIVEN. This means our trucks are in fact not optimally geared when delivered from the factory... Why I dont know.
I PERSONALLY gained 3-4MPH when going from 3.55's to 4.56's... with factory tire hight of 32.5" tall tires.
If you do the math... you will learn that our trucks are in fact OVERDRIVEN... and take the math even further you can find out what gearing would be best all round.
Keep in mind that RPM's alone do not dictate fuel economey... Its a very wide misconception many people seem to be stuck on. Its the load on the engine at any given RPM that effects MPG more then RPMs alone.
With that said, here are some math formulas you can use to assist you on your point.
Find your OVERALL GEAR RATIO:
REAR GEAR x OVERDRIVE GEAR RATIO = OVERALL GEAR RATIO
3.55 x .67 = 2.37 OGR
4.10 x .67 = 2.74 OGR
4.56 x .67 = 3.05 OGR
Im not sure about you... but as far as I can remember 3.05 gears where still considered to be a GRANNY GEAR! A 2.37 OGR (3.55's) is down right LUGGING and bad for fuel economey on anything larger then a car.
If you want to take it a bit further... do the math and find your RPM's at speed. It is a commonly known FACT that the 4.7L & 5.7L both see the best overal performance when the RPMs are 2000@60MPH... this will lead to your best overall fuel economey and in fact lead to GREAT off the line/towing performance. Its a "Having your cake & eating it to ZONE"....
SPEED x OGR x 336 / TIRE HIGHT = RPM
I hope you did not take this personal or as an attack..... take it as me turning to you and conversating about the subject... I know from my own and hundreds of other 3rd Gen Ram owners who in fact went to 4.56's... 99.9% of them have reported an increase in overall fuel economey over the 3.55's & 3.92... And NO they did not all have taller then stock tires.
SPEED SAFE, AIR RAM
Last edited by AIR RAM; Nov 27, 2008 at 02:54 PM.
Site Moderator
Joined: May 2008
Posts: 9,657
Likes: 24
From: Louisville, Ky
In town the lower gear will do better because it takes less effort for the engine to accelerate up to speed, thus using less energy. With the OD, the rpm will raise little thus putting the engine closer to max torque rpm which is more efficient. Going from a 3.92 gear to a 4.56 will not kill mileage at all.
You posted while I was replying Air Ram. Did you get my PM?
You posted while I was replying Air Ram. Did you get my PM?
Last edited by lxman1; Nov 27, 2008 at 03:01 PM.
All Star
Joined: Jan 2005
Posts: 852
Likes: 4
From: EULESS TEXAS DFW
Also I went from 3.55's to 4.56's... and gained 300 RPM's@60MPH... (THREE HUNDRED)... I can tell you that 300 RPMs will NOT kill your fuel economey. And it will allow your engine to HOLD overdrive and it will prevent the downshifting out of overdrive when taking on most hills... that alone will increase your MPG.
SPEED SAFE, AIR RAM
SPEED SAFE, AIR RAM
All Star
Joined: Jan 2005
Posts: 852
Likes: 4
From: EULESS TEXAS DFW
In town the lower gear will do better because it takes less effort for the engine to accelerate up to speed, thus using less energy. With the OD, the rpm will raise little thus putting the engine closer to max torque rpm which is more efficient. Going from a 3.92 gear to a 4.56 will not kill mileage at all.
You posted while I was replying Air Ram. Did you get my PM?
You posted while I was replying Air Ram. Did you get my PM?
SPEED SAFE, AIR RAM
Moderate User
Joined: Oct 2008
Posts: 17,003
Likes: 21
From: Albany, NY
Also I went from 3.55's to 4.56's... and gained 300 RPM's@60MPH... (THREE HUNDRED)... I can tell you that 300 RPMs will NOT kill your fuel economey. And it will allow your engine to HOLD overdrive and it will prevent the downshifting out of overdrive when taking on most hills... that alone will increase your MPG.
SPEED SAFE, AIR RAM
SPEED SAFE, AIR RAM
Here is the layout and "easy" mathematics that makes this true! It's not all the same but just bear with me as I cannot get into detail why I am using math like this or i will loose almost everyone. So in HankL form here we go...lol
A 33" tire has roughly 630revolutions per mile.
If you were going 60mph this would be true: 630x2.37final ratio=1493 That would be 1493rpms @60mph since were talking about rev per minute here.
Take the same tire of 630rev X 3.05final ratio = 1921
That's only 428rpms difference with that tall of a tire.
With a smaller tire, that number is practically multiplied.
Lets put it into a smaller tire say 245/45/17 with 811rev per mile like my mustang had stock with the same ratio's.
811x2.37=1922rpms
811x3.05=2473rpms
Using the same math on a smaller tire 25.6" generates 553more rpms which is 125rpms more than the 33" tire.
Also, $1500 is a bit steep for a gear install unless their gold plated gears???. Most places will charge $6-750 including parts!
All Star
Joined: Jan 2005
Posts: 852
Likes: 4
From: EULESS TEXAS DFW
Its clear that some people ASSUME and do not speak from MATH nor even experience...
Either one would arm you with the COMMON SINCE needed to grasp the concept. It all basically falls under MECHANICAL ADVANTAGE and simple math.
You need to take in ALL the variables to understand the out come... Again some of you guys stop at the rear gears and go not further. But you need to take and factor into the equation of the OVERDRIVE GEAR & TIRE HEIGHT & WEIGHT OF VEHICLE & SHAPE OF VEHICLE & AERODYNAMICS OF THE VEHICLE... Which all have an effect on the outcome of your gear selection.
A truck is shaped like a brick wall... so when in overdrive at 60MPH, your trucks gearing will determine weather it struggles move through at that speed or not... With a 2.37 (3.55) you had bet your lack of mechanical advantage will NOT be helping you at that speed... Sure in theory with no wind resistance it would make since... but not in the real world with wind resistance.
I almost forgot... HAPPY THANKSGIVING!
SPEED SAFE, AIR RAM
Either one would arm you with the COMMON SINCE needed to grasp the concept. It all basically falls under MECHANICAL ADVANTAGE and simple math.
You need to take in ALL the variables to understand the out come... Again some of you guys stop at the rear gears and go not further. But you need to take and factor into the equation of the OVERDRIVE GEAR & TIRE HEIGHT & WEIGHT OF VEHICLE & SHAPE OF VEHICLE & AERODYNAMICS OF THE VEHICLE... Which all have an effect on the outcome of your gear selection.
A truck is shaped like a brick wall... so when in overdrive at 60MPH, your trucks gearing will determine weather it struggles move through at that speed or not... With a 2.37 (3.55) you had bet your lack of mechanical advantage will NOT be helping you at that speed... Sure in theory with no wind resistance it would make since... but not in the real world with wind resistance.
I almost forgot... HAPPY THANKSGIVING!
SPEED SAFE, AIR RAM
Last edited by AIR RAM; Nov 27, 2008 at 05:19 PM.